The present invention relates to shear valves, in particular in a high performance liquid chromatography application.
In high performance liquid chromatography (HPLC, see e.g. http://en.wikipedia.org/wiki/HPLC), a liquid has to be provided usually at a very controlled flow rate (e. g. in the range of microliters to milliliters per minute) and at high pressure (typically 20-100 MPa, 200-1000 bar, and beyond up to currently 200 MPa, 2000 bar) at which compressibility of the liquid becomes noticeable. For liquid separation in an HPLC system, a mobile phase comprising a sample fluid with compounds to be separated is driven through a stationary phase (such as a chromatographic column), thus separating different compounds of the sample fluid.
Valves are commonly used in HPLC applications, e.g. injection valves for injecting a liquid sample into a high pressure flowing stream of liquid, a purge valves for positive displacement pumps, flow path switching valves, etc. Such valves used in HPLC applications are often multi-position rotary valve. Examples of multi-position rotary valve are disclosed in U.S. Pat. No. 4,068,528 A (two-position valves) or US 2003/0098076 A1 (multi-function rotary valves or random-access, dual, three-way, rotary switching valves).
Shear valves, which can be used in multi-way embodiments, are usually formed by a housing and a body defining a stepped cavity in which the rotor or seal is positioned. The housing contains at least two shear seal valve members positioned to be aligned with ports in the rotor (body) to establish communication between the shear seal means. Shear valves are usually provided as rotary valves (such as the aforementioned rotary valves) or translational valves (often also called sliding valves), such as disclosed in EP 0321774 A2.
A multi-way switching valve provides a means for selectively routing a fluid input flow to the valve to one of more alternate output flows from the valve. A rotary valve is of the type wherein fluid flow is directed by rotating a valve rotor element to discrete angular positions relative to a stationary valve stator element. A dual rotary valve provides two valves in one valve body, both simultaneously operated by the positioning of the valve rotor. Rotary switching valves are commonly used, for example, in HPLC and other analytical methods to selectively direct a flow stream of one or more fluids along alternate paths to an analytical device or containment vessel.
The aforementioned US 2003/0098076 A1 shows in its FIG. 1 a conventional type of dual, three-way, switching valve 220, which includes a disc-shaped rotor with a set of rotor grooves in the front face of the rotor that contacts, in a fluid-tight manner, the face of a cylindrically shaped stator body at a rotor-stator interface. Inlet passages and outlet passages, longitudinally bored through the stator body to the rotor-stator interface, are selectively fluidly coupled through the rotor grooves corresponding to the rotation of the rotor relative to the stator. Pivoting of the rotor enables the rotor grooves to fluidly couple selected passages of the stator, depending on their placement on the rotor and the angular position of the valve rotor. Model 7030 of Rheodyne, L. P. is an example of this type of switching valve.
WO 2006/056236 A1, EP 1520837 A1, and PCT/EP07/056735, all by the same applicant, show other types or embodiments of valves used in HPLC.
In the aforementioned documents, the stator of the valves is typically made of metal, such as stainless steel, and might comprise a stator seal (surfacing towards the rotor) made of a plastic-type material, such as an inert fluoropolymer, which is chemically inert, does not react with either the solvent or samples. In one embodiment of the U.S. Pat. No. 4,068,528 A, both the stator seal and a rotor seal (surfacing towards the stator) are formed of glass reinforced Tefzel with a chemical inertness approximately that of Teflon and glass and of sufficient mechanical strength to withstand high pressure, e.g., 50 MPa (7000 psi).
WO03074898 A1 relates to metal-ceramic composites for tribological uses and defined pairs based on such material. The friction heat generated between both sliding pairs and friction pairs has to be swiftly dissipated in order to maintain a lubricant film or ensure constant coefficients of friction. The document discloses metal-ceramic composites for friction/sliding uses, with basic compositions containing 30 to 75 percent by volume of one or several metallic phases, preferably aluminum and the alloys thereof, and 25 to 70 percent by volume of one or several non-metallic inorganic component/s as ceramic materials, preferably silicon carbide, aluminum oxide, titanium oxide, and silicates.
In modern HPLC with pressures rising up to 100 MPa and beyond, life time of valves becomes critical, in particular for the injection valve, as higher load on the rotor is required, which causes excessive wear.